The present invention relates to physiological monitoring and, more particularly, to acoustic ambulatory respiration monitoring.
Ambulatory respiration monitoring can be helpful in maintaining the respiratory health of people as they go about their daily lives. For example, continuous monitoring of respiration rate using a portable device can enable prompt discovery of a problem with the respiratory health of a person who suffers from a chronic pulmonary disease or works in hazardous environment so that the person can obtain timely treatment. Ambulatory respiration monitoring can also be useful for other purposes, such as senior monitoring and sleep monitoring.
Many different respiration monitoring systems are known. Some of these systems are airflow systems. In these systems, a subject breathes into an apparatus that measures the airflow through his or her mouth and respiration rate is estimated from the airflow. Other systems measure the subject's volume, movement or tissue concentrations. For example, in a respiratory inductance plethysmography (RIP) system, a subject wears a first inductance band around his or her ribcage and a second inductance band around his or her abdomen. As the subject breathes, the volumes of the ribcage and abdominal compartments change, which alter the inductance of coils, and the subject's respiration rate is estimated based on the changes in inductance. Unfortunately, these systems are much better suited for stationary monitoring than ambulatory monitoring.
Other respiration monitoring systems derive a subject's respiration rate from an electrocardiogram (ECG)-based wearable sensor. While these systems can be applied in ambulatory respiration monitoring, ECG-derived respiration rate measurements are highly sensitive to motion and often unreliable in ambulatory contexts.
For these reasons, many ambulatory respiration monitoring systems invoke the respiration sound method, sometimes called auscultation, to estimate a subject's respiration rate. In the respiration sound method, an acoustic transducer mounted on the body of the person being monitored captures and acquires an acoustic signal recording respiration sounds. The sound transducer is typically placed over the suprasternal notch or at the lateral neck near the pharynx because lung sounds captured in that region typically have a high signal-to-noise ratio and a high sensitivity to variation in flow. Once the acoustic signal with recorded respiration sounds has been generated, respiration phases are identified in the acoustic signal and respiration parameter estimates [e.g., respiration rate, inspiration/expiration (I/E) ratio] are calculated. Respiration health status information based on respiration parameter estimates may then be outputted locally to the monitored person or remotely to a clinician.
While ambulatory respiration monitoring systems that invoke the respiration sound method hold considerable promise, numerous obstacles to accurate respiration parameter estimation have arisen in these systems, including noise in the acoustic signal (both long-term background noise and short-term impulse noise), heart sound comingled with respiration sound in the acoustic signal, and variation in human respiration patterns.